1. Field of the Invention
The present invention relates generally to the field of telecommunications and, more particularly to a method and apparatus for providing a quality of service (QoS) based broadcast message scheduler for a CDMA wireless telecommunications system.
2. Description of the Related Art
FIG. 1 illustrates a schematic diagram of a portion of a typical wireless telecommunications system 100 and in particular, a code division multiple access (CDMA) wireless telecommunication system. The system 100 provides wireless communication service to a number of wireless terminals 101-1, 101-2, 101-3 that are situated within a graphical region. The heart of a typical wireless telecommunications system 100 is the Mobile Switching Center (MSC) 120, which may also be known as a Wireless Switching Center (WSC) or Mobile Telephone Switching Office (MTSO). Typically, the MSC 120 is connected to a plurality of base stations 103-1, 103-2, 103-3, 103-4, 103-5 that are dispersed throughout the geographic area serviced by the system 100 and to at least one Public Switched Telephone Network (PSTN) 130. The MSC 120 is responsible for, among other things, establishing and maintaining calls between wireless terminals and between a wireless terminal and a wireline terminal (not shown), which is connected to the system through local and/or long distance networks.
The geographic area serviced by the system 100 is partitioned into a number of spatially distinct areas called xe2x80x9ccells.xe2x80x9d In FIG. 1 each cell is schematically represented by a hexagon; in practice, however, each cell usually has an irregular shape that depends on the topology of the terrain serviced by the system 100. Typically, each cell contains a base station, such as for example base station 103-1, which includes the radios and antennas that the base station uses to communicate with the wireless terminals in that cell and also comprises the transmission equipment that the base station uses to communicate with the MSC 120.
For example, when wireless terminal 101-1 desires to communicate with wireless terminal 101-2, wireless terminal 101-1 transmits the desired information to base station 103-1, which relays the information to MSC 120. Upon receipt of the information, and with the knowledge that the information is intended for wireless terminal 101-2, the MSC 120 returns the information back to base station 103-1, which relays the information to the wireless terminal 101-2.
The MSC 120 is also connected to a short message service (SMS) message center (MC) 125. The SMS MC 125 provides SMS and broadcast short message service (BSMS) to the system 100. As known in the art, the BSMS allows the transmission of short text messages to multiple users within the system 100. When received, the text message is displayed on the user""s wireless terminal. Typically, the BSMS is used by the service provider for applications such as traffic and weather advisories, news and sports reports and mass advertisements.
In a CDMA telecommunications system information is transmitted over a traffic channel in fixed units of time referred to as frames. Each frame is typically twenty milliseconds long. Speech information is coded by a vocoder and transmitted in units referred to as speech frames, which have the same duration as the traffic frames on the CDMA traffic channel. The voice process of a user comprises alternating talk-spurt and silence periods, which are respectively reflected as voice data and breaks (i.e., no data) in the voice data of the speech frames. A BSMS message is transmitted on the forward traffic channel, i.e., base station to wireless terminal channel, along with voice information.
Each BSMS message is limited in size and delivered to a user in the form of data burst messages. Typically, the BSMS message is multiplexed into the traffic frame with the voice data by what is commonly referred to as a xe2x80x9cdim and burstxe2x80x9d method (i.e., where, depending upon the user""s vocoder mode, a minute portion of the voice data is chopped off or dimmed and the BSMS message information is used to fill in the breaks of the frame). It should be appreciated that the multiplexing of the BSMS message with speech information may be carried out in several ways depending upon the user""s service requirements.
It is desirable for the service provider to transmit BSMS messages to its users. It is also desirable for the users to receive the BSMS messages from the service provider. Unfortunately, the transmission of BSMS messages in a CDMA telecommunications system is not without its shortcomings. For example, signal interference between users of the CDMA system increases when the BSMS messages are multiplexed with the voice data. That is, since the breaks in the frame are now filled with the BSMS message information, extra radio frequency (RF) transmissions are required to transmit the traffic frames with the BSMS message in comparison to the RF transmission that would have been required to transmit the frame without the BSMS message. The extra RF transmissions are further compounded by the fact that the BSMS message is being transmitted to each user in the system. The extra RF transmissions to each user causes interference with the other users in the system. This interference dramatically effects the voice quality of the CDMA system.
Moreover, system capacity is also reduced by the transmission of BSMS messages. As is known in the art, in a CDMA wireless telecommunications system a base station process commonly referred to as xe2x80x9cpower controlxe2x80x9d regulates the transmitting power of wireless terminals communicating with the base station. The power control process also regulates the number of users that a cell can support at any one time based on the amount of noise or interference present within the cell. Since a CDMA wideband channel is reused in every cell, self interference caused by other users of the same cell and interference caused by users in other cells is the most limiting factor to the capacity of the cell and thus, the CDMA system. Due to fading and other channel impairments, maximum capacity is achieved when the signal-to-noise ratio (SNR) for every user is, on the average, at the minimum point needed to support an acceptable channel performance. Based on these and other principles, power control determines whether a new user (i.e., wireless terminal) or call can be added to a cell within the system. If power control determines that a new user or call cannot be added to a cell, it prevents the user from gaining access to the cell. Thus, the increased interference associated with the transmissions of the BSMS messages can also reduce the capacity of the CDMA telecommunications system.
Ensuring that a CDMA system operates to its full capacity while maintaining a high voice quality is extremely important for a CDMA service provider in terms of its revenue, customer satisfaction and reputation. As noted above, it is also desirable for the service provider to transmit BSMS messages and for the users to receive the BSMS messages. Accordingly, there is a desire and need to reduce the adverse impact on voice quality and system capacity attributable to the transmission of BSMS messages in a CDMA wireless telecommunications system.
In view of the foregoing shortcomings, and for other reasons, the present invention is directed to scheduling broadcast short message service (BSMS) messages in a manner that reduces the adverse impact on voice quality and system capacity, attributable to the transmission of the BSMS messages, in a wireless telecommunications system. The present invention comprises a computer implemented method and apparatus utilizing a quality of service (QoS) based broadcast message scheduler to negotiate and schedule the transmission times of the BSMS messages to the individual users in the system. The present invention also allows a user to tradeoff voice quality for broadcast capacity.
In one aspect of the present invention, a method for scheduling a transmission time of a message to be transmitted in a telecommunications system is provided. The method includes the steps of: computing a respective first message valid time period for at least one sector in the telecommunications system based on a length of the message, a second message valid time period and number of users in the respective at least one sector, said second message valid time period being associated with the message; and scheduling a respective transmission time of the message in the at least one sector based on the computed respective first message valid time period.
In another aspect of the present invention, a wireless telecommunications system is provided. The system includes: a mobile switching center, said mobile switching center including a first programmed processor for scheduling a transmission time of a message to be transmitted in said system and for computing a first message valid time period for a sector in said system based on a length of the message, a second message valid time period and number of users in the sector, said second message valid time period being associated with the message; and a base station coupled to said mobile switching center, said base station comprising a second programmed processor for scheduling a respective transmission time of the message for at least one user in the sector based on the computed first message valid time period.
It is an object of the present invention is to provide an apparatus for negotiating and scheduling the transmission times of BSMS messages to users in a wireless telecommunications system.
It is another object of the invention to provide an apparatus for negotiating and scheduling the transmission times of BSMS messages to users in a wireless telecommunications system that allows a user to tradeoff voice quality for broadcast capacity, if so desired.
It is a further object of the present invention to provide a method for negotiating and scheduling the transmission times of BSMS messages to users in a wireless telecommunications system.
It is yet another object of the invention to provide a method for negotiating and scheduling the transmission times of BSMS messages to users in a wireless telecommunications system that allows a user to tradeoff voice quality for broadcast capacity, if so desired.